The Positive Crankcase Ventilation (PCV) valve is a part of the PCV system where the engine passes harmful crankcase combustion gases to the air intake. Instead of venting the crankcase gases to the atmosphere, they are fed into the intake manifold where they can be re-entered into the engine combustion chambers as part of the air/fuel mixture and burned. This results in lower pollution and extended engine oil life. PCV valves act as both a crankcase ventilation system and as a pollution control device.
The PCV valve performs a complicated, but necessary, control function and can act to restrict the amount of air passing through it. When the engine is running under light loads, the intake manifold air pressure is less than the crankcase air pressure. Under these conditions, the crankcase gases are drawn through the PCV valve and into the intake manifold.
At idle, the intake manifold vacuum is near maximum. This results in the least amount of blow-by and the PCV valve provides the largest amount of restriction. As engine load increases, vacuum on the valve decreases proportionally and blow-by increases proportionally. At a low level of vacuum, the PCV valve allows more air flow.
When the engine is running at wide open throttle, the manifold pressure is about the same level as the engine crankcase, and the function of the PCV valve is minimal. When the manifold pressure is considerably higher than that of the crankcase, the PCV valve is closed to prevent reversal of the exhausted gases back into the crankcase.
The operation of a turbocharger in a turbocharged engine is similar to that of an engine running at wide open throttle. During boost from a turbocharger, additional pressure is built up that needs to be relieved.
It is an object of the present invention to provide an improved PCV valve for use in engine systems which have turbochargers.